Stilbene synthase (EC 2.3.1.95) is a polyketide synthase catalyzing the synthesis of 3,4'. 5-trihydroxystilbene (resveratrol) from p-coumaroyl-CoA and three molecules of malonyl-CoA. This cytosolic enzyme is confined to a few plant genera. In intact and unchallenged cells, the enzyme is weakly expressed, but it is synthesized de novo upon attack by pathogens. Pathogen-derived elicitors turn on the synthesis of stilbene phytoalexins, which are part of the process of induced resistance in these plants. In grapevine, resveratrol and other hydroxystilbenes with fungicidal potential are the dominating phenols produced under biotic stress.
Several plants including grapevine synthesize resveratrol when attacked by pathogens. Comparative studies have revealed that the model of response against microbial attack depends primarily on the developmental stage of the individual plant cell. In this respect, the systems in parsley, bean, and potato have been established and compared with each other; each individual plant species, is unique with regard to the rate at which gene expression is changed, the duration of the transient stage, and the extent to which the enzymes of the pathway are coordinately produced. Stilbenes with fungicidal potential are formed in several unrelated plant species, such as peanuts (Arachis hypogaea), grapevine (Vitis vinifera), pine (Pinus slvestris) and orchids. A few plants such as spruce and rhubarb contain stilbenes but do not exhibit increased de novo syntheses of stilbenes in response to elicitors.
In grape, stilbenes (resveratrol and its oligomeric derivative viniferin) have antimicrobial activity against Botrytis cinerea and Plasmopara viticola, the main pathogens of this species. Liswidowati et al, (Planta (1991) 18: 307-314) demonstrated that stilbene synthase is rapidly and transiently synthesized in grape cell cultures after elicitation with B. cinerea. A clone for grape stilbene synthase has been isolated and it has recently been shown that stilbene synthase, when expressed in transgenic tobacco plants, confers an increased disease resistance against B. cinerea.
Temporal expression of stilbene synthesis in grape has been studied by analyzing RNAs present at different stages of elicitation by addition of Phytophthora camelivora cell wall to cultures of Vitis vinifera. Stationary mRNA levels reached maximal values (approximately 15-fold baseline) 6 hours after the onset of elicitor treatment. It therefore would be of interest to obtain the gene encoding this early onset stilbene synthase and isolate the regulatory elements responsible for the rapid and high level of expression of the coding sequence; the regulatory elements provide a means for controlling gene expression for plant disease and stress resistance.
There is substantial interest in modifying a plant with promoters to afford biotic or abiotic stress-induced transcription and expression of a gene introduced into the plant. Of particular interest are promoters which provide for locally inducible expression of genes. Also of interest is the ability to enhance or modify the properties of other promoters.